I play another role playing game with a world similar to the size this seems it will be and it plays horribly with 32 people. With that said 100 people per server would be a good number I would think. If it can handle more I wouldn't mind seeing the dynamic!
Patience is key guys, We are all itching to get our hands on this amazing looking game and I bet most of you are like me and see potential with it being an amazing game!! A quality product takes time. I'm anxious as well!
And yet here you still are. So many times I've seen people complain and be adamant the game is never coming out yet you're still here. If you don't believe in any way the game will succeed then go and get your refund.